If you thank your parents for your intelligence or blame them for your stupidity, you might be right—but not because of the way they raised you. In fact, a new study provides the most compelling evidence yet that intelligence is affected by a single gene.

The research, carried out at UCLA and published in Nature Genetics, studied fMRI brain scans and DNA samples of over 20,000 people. Thanks to the massive pool of volunteers, the researchers were able to identify a single gene that has a significant, measurable—but admittedly small—impact upon intelligence.

They found that variations on a gene called HMGA2 can alter IQ by 1.29 points. The variation in the gene is just a single different molecule in its string of DNA. Despite the small difference, it's an amazing discovery to establish that such a small chemical variation can have an effect on human intelligence.

In fact, as well as raising IQ score by 1.29 points, the same gene variation also increases the overall volume of the brain by 0.58 per cent of average brain size—that's equivalent to about two extra teaspoons of brain power.

It's worth noting that the effect is small, and required a huge population of participants to identify. That means that it doesn't have a huge impact on the way we judge each other's intelligence—but it does for the first time demonstrate that single genetic differences have a role to play in determining our cognitive abilities. [Nature Genetics via New Scientist]